That is because Monero's difficulty adjustment algorithm takes several blocks to adjust with the network hashrate. iirc it takes 720 blocks for Monero to adjust the difficulty according to Network hashrate (it's not linear tho)
Difficulty in fact is dependent on Network hashrate. It depends on coin to coin and what difficulty adjustment algo they use.
This right here. You just took like four short sentences to say what I spent paragraphs trying to explain.
Technically, from my reading, difficulty is driven by predefined time to find last set of blocks. If it takes more time, and difficulty will adjust lower, and vice versa if time is lessor than predefined then difficulty will adjust higher.
Hash-rate does not factor directly into difficulty calculation, but only in-directly in the sense that more hash-rate in the network will mean that time to find blocks will be lessor, and lessor time will lead to increase in difficulty.